Measurement system cluster

ABSTRACT

Systems and methods are disclosed for measuring semiconductor wafers in a fabrication process using one or more of a plurality of measurement systems. A measurement system cluster is provided having a plurality of such measurement systems, along with a system for transferring wafers to one or more of the measurement systems according to one or more selection criteria. Measurement systems may be selected for use based on availability and throughput capabilities, whereby overall system throughput and efficiency may be improved within the required accuracy capabilities required for measuring process parameters associated with the wafers.

PRIORITY CLAIM

This application is a Divisional of U.S. patent application Ser. No.10/132,538, filed Apr. 24, 2002 now U.S. Pat. No. 6,999,164 and claimspriority to U.S. Provisional Application Ser. No. 60/286,485, filed Apr.26, 2001, both of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to the art of semiconductor devicemanufacturing and fabrication, and more particularly to systems andmethodologies for measuring process parameters associated with processedsemiconductor wafers.

BACKGROUND OF THE INVENTION

In the semiconductor industry there is a continuing trend toward higherdevice densities. To achieve these high densities there have been, andcontinue to be, efforts toward scaling down the device dimensions onsemiconductor wafers. In order to accomplish such a high device packingdensity, smaller feature sizes are required. These may include the widthand spacing of interconnecting lines and the surface geometry such asthe corners and edges of various features.

The requirement of small features with close spacing between adjacentfeatures requires high-resolution photo-lithographic processes as wellas high resolution metrology and inspection instruments and systems. Ingeneral, lithography refers to processes for pattern transfer betweenvarious media. It is a technique used for integrated circuit fabricationin which, for example, a silicon wafer is coated uniformly with aradiation-sensitive film (e.g., a photoresist), and an exposing source(such as ultraviolet light, x-rays, or an electron beam) illuminatesselected areas of the film surface through an intervening mastertemplate (e.g., a mask or reticle) to generate a particular pattern. Theexposed pattern on the photoresist film is then developed with a solventcalled a developer which dissolves either the exposed or unexposeddepending on the type of photoresist (i.e., positive or negative resist,thus leaving a photoresist pattern corresponding to the desired patternon the silicon wafer for further processing.

In addition to lithographic processes, other process steps in thefabrication of semiconductor wafers require higher resolution processingand inspection equipment in order to accommodate ever shrinking featuresizes and spacing. Measurement instruments and systems are used toinspect semiconductor devices in association with manufacturingproduction line quality control applications as well as with productresearch and development. The ability to measure and/or view particularfeatures in a semiconductor workpiece allows for adjustment ofmanufacturing processes and design modifications in order to producebetter products, reduce defects, etc. For instance, device measurementsof critical dimensions (CDs) and overlay registration may be used tomake adjustments in one or more such process steps in order to achievethe desired product quality. Accordingly, various metrology andinspection tools and instruments have been developed to map and recordsemiconductor device features, such as scanning electron microscopes(SEMs), atomic force microscopes (AFMs), scatterometers, spectroscopicellipsometers (SEs), and the like. Scatterometers, as used in thiscontext, are optical instruments that employ algorithms to invert theparameters of a grating from the measured optical characteristics.Typically, scatterometers are used to measure gratings with lateraldimensions that are finer than wavelengths employed by the instrument.The fundamental optical instrument for a scatterometer may be identicalto optical instruments used, e.g., for thin-film metrology. Thus an SE,which is routinely used to characterize thin (unpatterned) films, may beemployed as a scatterometer if the appropriate algorithms are available.The same would be true of a reflectometer. In some cases, the opticalinstrument portion of a scatterometer may be specifically designed forscatterometry. In what follows, “SE” is used to designate aspectroscopic ellipsometer used for standard thin film measurements,i.e., film thickness and/or optical properties.

Such measurement instruments are typically employed in stand-alone,off-line fashion, for example, wherein one or more wafers processed by aparticular process tool are measured or inspected and a determination ismade as to whether measured process parameters (e.g., CDs, overlayregistration, film thicknesses, material properties, particle count) arewithin acceptable limits, and/or whether process related defects arepresent in the wafers. A stand-alone measurement instrument is notintegrated into a process tool, and thus can be used to service multipleprocess tools. The measurements or inspection may be performed usingmore than one such measurement instrument, where features are measuredusing different instruments. Because the measurement instruments arestand-alone systems, the wafers must be transported between the processtool and the measurement instruments before a measurement can beobtained. The stand-alone nature of conventional measurementinstrumentation and the resulting transport of wafers between suchinstruments results in significant down-time in a semiconductorfabrication facility, wherein expensive process tools are shut downpending a final determination as to the existence of problems in theprocess.

In addition, where wafers must be measured in two or more successivemeasurement systems in serial fashion, the measurement instrument havingthe lowest wafer throughput capacity becomes a bottleneck for theinspection process, thus further exacerbating process down-time.Moreover, existing measurement or inspection instruments forsemiconductor wafer fabrication processes may provide different resultsfor measurement of the same feature, wherein one instrument may identifya dimensional problem associated with a particular feature, whileanother such instrument may not. Thus, there is a need for improvedmeasurement systems and methodologies which provide for timely,consistent feature measurement and inspection for wafers being processedin a fabrication facility, and which reduce or mitigate processdown-time.

SUMMARY OF THE INVENTION

The following presents a simplified summary of the invention in order toprovide a basic understanding of some aspects of the invention. Thissummary is not an extensive overview of the invention. It is intended toneither identify key or critical elements of the invention nor delineatethe scope of the invention. Rather, the sole purpose of this summary isto present some concepts of the invention in a simplified form as aprelude to the more detailed description that is presented hereinafter.The present invention provides systems and methods for measuring andinspecting semiconductor wafers in a fabrication process using one ormore of a plurality of measurement instruments or metrology tools bywhich the aforementioned shortcomings associated with prior systems maybe mitigated. Clustered measurement systems are provided having aplurality of measurement instruments, together with systems fortransferring wafers to one or more of the measurement devices accordingto selection criteria. Measurement systems may accordingly be selectedfor use based on availability, throughput, capabilities and/or otherconsiderations, whereby overall system throughput and efficiency may beimproved within the accuracy capabilities required for measuring processparameters (e.g., such as CDs, overlay registration, or the like)associated with the wafers.

In addition, the present invention facilitates correlation orcross-calibration between data responses of at least two measurementsystems, such as for example a CD-SEM and a scatterometer. Inparticular, a wafer (e.g., one or more layers in layer stack) may bemeasured with a scatterometer to receive a data response associated withthe scattering of an incident wavelength of light. The wafer may also bemeasured by a CD-SEM to receive another data response, which ischaracteristic of the CD-SEM device. The data responses from thescatterometer and the CD-SEM may be correlated. Based on thecorrelation, the scatterometer can be adjusted to the extent that futuremeasurements taken by a scatterometer resemble data responses as ifproduced by a CD-SEM. This correlation facilitates alternating orvarying between the measurement system employed depending on theprocessing time, costs, accuracy and efficiency needs and requirements.

According to one aspect of the present invention, a measurement systemcluster is provided having two or more measurement instruments such asscanning electron microscopes (SEMs), atomic force microscopes (AFMs),scatterometers, spectroscopic ellipsometers (SEs), or the like, whichcan be selectively employed to measure process parameters associatedwith a wafer. The various instruments may be interconnected to shareinformation, such as calibration information, and can becross-calibrated. The metrology cluster further comprises a wafertransfer mechanism or system, such as a robot, operative to selectivelyprovide a wafer to one or more of the measurement devices according toat least one measurement system selection criterion. The selectioncriteria, for example, may take into account the capabilities,availability, and throughput of the various measurement instruments,whereby a selected measurement device has appropriate measurementcapabilities required for a given wafer (e.g., or set of wafers beingprocessed), such that an available measurement instrument having thehighest throughput capacity can be selected for use in performing therequired measurements.

In addition, the present invention facilitates correlation orcross-calibration between measurements of at least two measurementsystems, such as for example a CD-SEM and a scatterometer. Inparticular, multiple reference samples, e.g., a particular site indifferent dies on a reference wafer, may be measured with ascatterometer. The reference sites may also be measured by a CD-SEM. Themeasurements from the scatterometer and the CD-SEM may be correlated.Based on the correlation, future scatterometer measurements, e.g., onproduction samples, can be adjusted to resemble measurements that wouldbe produced by a CD-SEM. This correlation facilitates alternating orvarying between the measurement system employed depending on theprocessing time, costs, accuracy and efficiency needs and requirements.

Another aspect of the invention provides a wafer measurement orinspection system having a measurement instrument operative to measureat least one process parameter associated with a wafer, as well as anoptical character recognition (OCR) system providing a waferidentification according to at least one optically recognizablecharacter on the wafer. A character in this context is taken as anindicator of information. For examples, characters may be alpha-numericor a bar code. The OCR system may thus read stampings or markings, suchas lot numbers, data codes, and other character-based indicia on thewafer being measured, and provide for selection of measurementinstruments appropriate for the required measurement task. Themeasurement system, moreover, may be integral with one or more processtools forming a part of the fabrication process, whereby processedwafers are provided directly to the system without further machine orhuman intervention.

In accordance with yet another aspect of the invention, there isprovided a methodology for measuring process parameters associated witha wafer in a semiconductor fabrication process. Wafers are received fromthe fabrication process and selectively provided to one or moremeasurement instruments according to a measurement system selectioncriteria. In this regard, the selection criteria can include using anavailable measurement instrument having the highest throughput capacityand the required accuracy or other performance capabilities required forthe wafer measurements, whereby the overall throughput of a system canbe improved. The method may further include identifying the wafer beingmeasured, such as for example, through reading one or more opticalcharacters on the wafer, determining measurement capabilities requiredto measure the process parameter according to the identity of the wafer,and selecting the appropriate measurement instrument according to therequired measurement capabilities and measurement system capabilitiesinformation associated with the available measurement devices.

To the accomplishment of the foregoing and related ends, the invention,then, comprises the features hereinafter fully described. The followingdescription and the annexed drawings set forth in detail certainillustrative implementations of various aspects of the invention.However, these implementations are indicative of but a few of thevarious ways in which the principles of the invention may be employed.Other aspects, advantages and novel features of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating an exemplary measurementsystem cluster in accordance with one or more aspects of the presentinvention;

FIG. 2 is a schematic diagram illustrating a fabrication process havingprocess tools and stand-alone measurement systems;

FIG. 3 is a schematic diagram illustrating a fabrication process havingan exemplary measurement system cluster in accordance with theinvention;

FIG. 4 is a schematic diagram illustrating a semiconductor waferfabrication process employing measurement system clusters providingmeasurement information as feedback to associated process tools, as wellas to an advanced process control system according to the invention;

FIG. 5 is a schematic diagram illustrating another exemplary measurementsystem cluster operatively associated with a process tool and anadvanced process control system;

FIG. 6 is a schematic diagram illustrating another exemplary measurementsystem cluster in operative communication with a process tool;

FIG. 7 is a schematic diagram illustrating another exemplary measurementsystem cluster integrated into a fabrication process with a process tooland an APC system;

FIG. 8 is a schematic diagram illustrating an exemplary measurementsystem selection logic component according to another aspect of theinvention; and

FIG. 9 is a flow diagram illustrating an exemplary methodology inaccordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

The various aspects of the present invention will now be described withreference to the drawings, wherein like reference numerals are used torefer to like elements throughout. The invention provides systems andmethods for measuring and/or inspecting semiconductor wafers in afabrication process using one or more of a plurality of measurementinstruments or systems. A measurement system cluster is provided havinga plurality of such measurement systems, together with a system fortransferring wafers to one or more of the measurement systems accordingto one or more selection criteria. Measurement instruments or systemsmay be selected for use based on availability and throughputcapabilities, whereby overall equipment throughput and efficiency can beimproved within the accuracy capabilities required for measuring processparameters associated with the wafers.

In FIG. 1, an exemplary measurement system cluster 2 is illustrated inwhich various aspects of the present invention may be implemented. Thecluster 2 may be advantageously employed for measuring processparameters (e.g., overlay registration, photoresist layer defects,feature sizes, spacing between features, particle defects, chemicaldefects, and the like) associated with wafer 4 in a semiconductorfabrication process. The measurement system cluster 2 comprises aplurality of measurement systems 10, 12, and 14 having measurementinstruments (not shown) associated therewith. For example, the systems10, 12, and 14 may include scanning electron microscopes (SEMs), atomicforce microscopes (AFMs), scatterometers, spectroscopic ellipsometers(SEs), or other measurement instruments adapted to measure processparameters associated with processed semiconductor wafers 4.

The cluster 2 further comprises a wafer transfer system 20, such as arobot or other automated wafer translation device, which receives wafers4 processed in the fabrication process via an unloader station 22 whichunloads wafers 4 from a cassette 24 or other wafer carrying device. Thewafer transfer system 20 then selectively provides the wafers 4 to oneor more of the measurement systems 10, 12, and/or 14 according to ameasurement system selection criteria as described in greater detailhereinafter. One or more process parameters (not shown) are thenmeasured and/or inspected in order to verify proper processing of thewafers and/or to detect defects or errors in the fabrication process.The exemplary cluster system 2 further comprises a computer system 30having a measurement system selection logic 34, and calibrationinformation 36 therein. The measurement systems 10, 12, and 14, as wellas the unloader station 22, the wafer transfer system 20, and thecomputer system 30 are networked together via a network 40, wherebymeasurement information, measurement system selection information,calibration information 36, and other control information and data maybe shared between the various components of the measurement systemcluster 2.

Once the appropriate process parameters associated with the wafers 4have been measured via the measurement systems 10, 12, and/or 14, thewafer transfer system 20 provides the wafers 4 to a loader station 42which loads the wafers into outgoing wafer cassettes 24 for transfer toother systems in the fabrication process, such as a downstream processtool (not shown). There are many alternative arrangements, each havingdifferent strategies for loading and unloading wafers. For instance, thestations 22 and/or 42 can be loader/unloader stations, able to performboth functions. With a loader/unloader station, wafers may be returnedafter measurement to the same cassette in which they arrived. Inaddition, cluster 2 may have a single loader/unloader, or more than two;and/or cluster 2 may have more than one each of load and/or unloadstations.

The cluster 2 further comprises an optical character recognition (OCR)system 44 providing a wafer identification (not shown) to themeasurement system selection logic component 34 via the network 40,whereby the component 34 may make an appropriate selection ofmeasurement system(s) 10, 12, and/or 14 to be used to measure or inspectthe wafer 4. Although the exemplary cluster 2 identifies the wafers 4using the OCR system 44, other techniques may be used to identify thewafers 4, such as for example, location within the cassette 24, or othermethods as are known. It will be appreciated, however, that where lotcode information, date codes, and the like are printed or stampeddirectly on the wafers 4, the OCR system 44 advantageously reduces thelikelihood of incorrect wafer identification.

The measurement system selection logic component 34 in the computersystem 30 provides a measurement system selection to the wafer transfersystem 20 according to one or more selection criteria (e.g., asillustrated and described in greater detail hereinafter with respect toFIG. 8), wherein the wafer transfer system 20 provides the wafers 4 toat least one of the measurement systems 10, 12, and/or 14 according tothe measurement system selection. For example, the measurement systemselection criteria can include capabilities requirements informationassociated with the wafer 4, as well as capability information,availability information, and throughput information associated with themeasurement systems 10, 12, and 14. The selection moreover, may be madeaccording to a desired sequencing of measurements in the systems 10, 12,and/or 14.

The capabilities information may thus be derived according to the waferidentification from the OCR system 44, and may comprise informationindicating the type of feature(s) or dimension(s) to be measured in thesystem 2, as well as the required accuracy for the measurement(s). Themeasurement system selection from the logic component 34 may furthertake into account the measurement capabilities of the variousmeasurement systems 10, 12, and/or 14. For example, one or more of thesystems 10, 12, and/or 14 may be capable of performing a givenmeasurement within the required accuracy, while others may not. Inaddition, the respective systems 10, 12, and/or 14 can each havedifferent throughput capabilities. For instance, a SEM instrument may beable to measure 30 wafers per hour (wph), a scatterometer may measure upto 150 wph, and a spectroscopic ellipsometer may measure 75 to 80 wph.In selecting a measurement system to perform a given measurement task,therefore, the measurement system selection logic component 34 mayadvantageously select the system which can provide the highestthroughput, within the required measurement capabilities for themeasurement.

In this regard, the selection logic component 34 may also consider whichsystems 10, 12, and/or 14 are currently available in scheduling thetransfer of wafers 4 via the transfer system 20. Thus, the measurementsystem selection logic component 34 provides the selection indicating aselected measurement system 10, 12, or 14 having capabilities requiredfor the wafer 4 according to the capabilities requirements information(e.g., obtained or derived from the wafer identification via the OCRsystem 44) and the measurement system capability information.Furthermore, the selection may reflect the measurement system having thehighest throughput with the capabilities required for the wafer 4according to the measurement system availability information and thethroughput information.

As the various measurement systems 10, 12, and 14 are interconnected inthe cluster 2, and may share information via the network 40, the systems10, 12, and/or 14 may be cross-calibrated. In this regard, thecalibration information 36 in the computer system 30 may be sharedbetween the various systems 10, 12, and 14, whereby the measurementsmade by one measurement instrument in the systems 10, 12, or 14, arecomparable to those made by another such instrument. The exemplarycluster system 2 thus provides significant advantages over conventionalstand-alone measurement systems with respect to cross-calibration aswell as in reducing excess transferring of the wafers 4 between suchstand-alone measurement stations in a fabrication process.

Information may be provided to an upstream (e.g., or downstream) processtool (e.g., photo-resist track, stepper, or the like), which can employsuch information as process feedback (or feed forward), whereby on-lineclosed-loop process control can be achieved, for example, wherein theprocess tool performs fabrication processing steps according to themeasurement data in order to mitigate defects in processed wafers 4.Alternatively or in combination, the measurement (e.g., and/or defectdetection) information may be provided to an advanced process control(APC) system (not shown), which in turn may provide process adjustmentsto such process tools in feedback and/or feed forward fashion. In thisregard, it will be appreciated that the reduction in transfer timeresulting from clustering of multiple measurement systems 10, 12, and 14into a single system 2, as well as the selective employment ofappropriate measurement systems based at least in part on throughputand/or availability information, may be used to mitigate down-time ofrelated process tools, whereby real-time or near real-time measurementand/or defect detection may be achieved with little or no fabricationprocess down-time, in accordance with the present invention. Moreover,the exemplary measurement cluster 2 may also be integrated with aprocess tool, as illustrated further in FIGS. 6 and 7, which operates toperform one or more fabrication processing steps on the wafers 4 and toprovide the processed wafers 4 to the wafer transfer system 20.

Referring briefly to FIG. 2, a portion of a conventional waferfabrication process 50 is illustrated in which wafers 54 proceed inserial fashion from a first process tool 56 to a series of measurementinstrument systems 58, 60, and 62. The systems 58, 60, and 62 providemeasurement information to an APC system 64, which in turn providesfeedback information 66 (e.g., such as a process adjustment or controlinformation) to the process tool 56. Thereafter, the wafers 54 areprovided to a second (e.g., downstream) process tool 68. As can be seenin FIG. 2, the APC system 64 is unable to provide timely feedback to theprocess tool 56 because the measurements from the measurement systems58, 50, and 62 are not made at the same time, and further because thewafers 54 must be transported (e.g., typically manually) between thesystems 58, 60, and 62.

Referring now to FIG. 3, the invention provides clustering ofmeasurement instruments or systems 71, 72, and 73 into a measurementsystem cluster 70 along with a wafer transfer system 74, wherein thecluster or system 70 may receive wafers 75 from an upstream process tool76 in a fabrication process 80, typically in a cassette or FOUP. Thesystem 70 may operate in a manner similar to the operation of theexemplary cluster 2 of FIG. 1, whereby the wafer transfer system 74selectively provides the wafers 75 from the process tool 76 to one ormore of the measurement systems or instruments 71, 72, and/or 73according to one or more measurement system selection criteria. Themeasurement system selection criteria may include, for example,measurement capabilities, measurement capability requirements,availability, anticipated need based on scheduling of fabricationprocess 80 and/or throughput capabilities. The time savings achieved bythe clustering of the measurement systems 71–73 and the operation of thewafer transfer system 74 in selecting an appropriate measurement systemfor a particular inspection task allows timely provision of measurementinformation (e.g., overlay registration, CD measurements, feature sizeand spacing) for feedback 78 to the process tool 76 in a timely fashion,whereby the down-time associated with process parameter measurement inconventional systems (e.g., FIG. 2) can be advantageously mitigated inaccordance with the present invention. Once measured, the wafers 75 canthen be provided from the measurement system cluster 70 to a second(e.g., downstream) process tool 79. Although not shown, the measurementinformation may be used for feed forward, e.g., to downstream processtool 79. System 70 provides the same advantages over a series ofmeasurement instrument systems 58, 60, and 62, as shown in FIG. 2, whenused for feed forward or feedback information.

Another semiconductor device fabrication process 100 is illustrated inFIG. 4, in which other advantages of the present invention are shown.The process 100 comprises process tools 102, 104, and 106 and associatedmeasurement system clusters 112, 114, and 116, respectively, whichoperate to measure one or more process parameters associated with wafers110 in a manner similar to the exemplary system 2 of FIG. 1. Any ofmeasurement system clusters 112, 114, and 116 may be a cluster of onemeasurement system. Further, the association of a cluster with a tool,e.g., cluster 112 to tool 102, can be integrated into the tool, wherethe cluster shares support, wafer transport and/or other facilities. Themeasurement system clusters 112, 114, and 116, as well as the processtools 102, 104, and 106 communicate with each other via a network 120,whereby information may be transferred therebetween. An APC system 130is also operatively connected to the network 120, such that measurementinformation (e.g., CDs, overlay registration, and the like) may beobtained from the measurement systems 112, 114, and 116 for providingprocess feedback or process feed forward or adjustments to the variousprocess tools 102, 104 and/or 106 and for other processing of suchmeasurement information. For example, the APC system 112, may providedefect classifications to one or more of the process tools 102, 104,and/or 106, whereby adjustments may be made therein, in order to reducethe number of such defects in the fabrication process 100.

The measurement system clusters 112, 114, and 116 can also include APCsystems therein, providing feedback information 122, 124, and 126,respectively to the process tools 102, 104, and 106, for timelyadjustment of the individual process tools 102, 104, and 106, and therespective process steps carried out therein. Alternatively or incombination, such feedback information may be provided from themeasurement system clusters 112, 114, and/or 116 to one or more of theprocess tools 102, 104, and/or 106 via the network 120. In addition, theinvention provides for sharing of calibration information between theclusters 112, 114, and/or 116, whereby the clusters 112, 114, and/or 116and/or the component measurement instrument systems therein, may becross-calibrated, such that the measurements made thereby are performedaccording to a universal standard across the entire process 100. Theuniversal standard may apply over a larger domain than just process 100,e.g., within a whole manufacturing facility, or even linkingmanufacturing facilities.

The process 100 can further include a standalone measurement systemcluster 150 networked with the clusters 112, 114, and 116 via network120. For example, clusters 112, 114, or 116 may be integrated withintheir associated tools, as described above, and primarily measure wafers110 processed by their associated tool, whereas cluster 150 is set upfor measuring wafers from many sources with ease. Furthermore, cluster150 may comprise measurement instruments (not shown) of types found inthe clusters 112, 114, and 116 as well as a recipe generator 152, adatabase generator 154 and a defect classification system 156. Recipesare sets of instructions for a measurement instrument comprising whereto measure on the wafer, measurement system parameters for the physicalmeasurement, and specification of an algorithm to convert thefundamental physical measurements into useful information. For example,for a reflectometer measurement instrument, the recipe may compriseinformation about the layout of the wafer including die size andlocation, which dies on the wafer to measure, one or more sites withinthe die at which to measure (typically referenced to structures in thedie), pattern recognition parameters to identify and locate thestructures in the die, the length of time to integrate over formeasuring reflected intensities, the wavelengths of light at which toreport measured intensities, an algorithm based on model that comprisesa stack of thin films at the measurement location, specification ofwhich parameters are known and which are to be measured, etc. The recipemay comprise much more information than cited in this example.Instruments of a different nature than the exemplary reflectometer mayrequire rather different information in their appropriate recipes.

In general, databases contain information to aid in the conversion ofthe fundamental physical information collected by an instrument intouseable information about the process state of the wafer. As an example,a database for a reflectometer from database generator 154 can aid inconverting measured optical absolute reflectivities to CD or filmthickness. Algorithms use databases, e.g., for scatterometry, when thecomputational time for an algorithm is excessive, and it is useful tostore partial results of the algorithm in a database for later,accelerated use. The cluster 150 can be employed to generate databasesand/or recipes for the measurement and/or inspection of wafers by theinstruments of the in-process measurement system clusters 112, 114,and/or 116, which may be uploaded thereto through the networks 120. Inthis manner, the stand-alone cluster 150 may be advantageously employedto perform setup operations (e.g., recipe and/or database generator) foruse in the in-process clusters 112, 114 and/or 116, while the clusters112, 114, 116 are in use measuring processed wafers.

Referring now to FIG. 5, another exemplary implementation of the presentinvention is illustrated, wherein a measurement system cluster 202 ispart of a fabrication process 200 having a process tool 204 and an APCsystem 206. The systems 202 and 206, as well as the process tool 204 maycommunicate with each other via a network 208. Alternatively or incombination, the APC system 206 can communicate directly with themeasurement system cluster 202. The measurement system cluster 202 isemployed in the process 200 for measuring process parameters associatedwith wafers (not shown) transferred thereto from the process tool 204 ina manner similar to the exemplary system 2 of FIG. 1. The system 202includes a scanning electron microscope (CD-SEM) system 210 operative tomeasure process parameters of the wafers, which may also comprise pumpsand sealing devices (not shown) for creating a vacuum therein. Thesystem cluster 202 further includes an optical scatterometer 212 and aspectroscopic ellipsometer (SE) 214, to which a robot 216 mayselectively provide wafers according to one or more selection criteria,as illustrated and described hereinabove. As noted above, opticalscatterometer 212 may comprise spectroscopic ellipsometer 214. Opticalscatterometer 212 may also comprise a reflectometer.

Wafers are provided to the robot 216 by an unload station 220, forexample, which unloads the wafers from a wafer holding device such as acassette (not shown), and once appropriate measurements have been madein the integrated system 202, the wafers may be loaded into appropriatecassettes at a loading station 222. As with the measurement systemsillustrated and described above, the robot 216 of the system 202selectively provides wafers to one or more of the component measurementsystems or instruments 210, 212, and/or 214 according to at least oneselection criterion, such as capabilities requirements informationassociated with the processed wafers, as well as capability information,availability information, and throughput information associated with themeasurement systems 210, 212, and 214.

There are many alternative arrangements, each having differentstrategies for loading and unloading wafers, as described above inconjunction with FIG. 1.

The capabilities information can comprise information indicating thetype of feature(s) or dimension(s) to be measured in the system 202, aswell as the required accuracy for the measurement(s). The selectiontakes into account the measurement capabilities of the systems 210, 212,and/or 214. For example, one or more of the systems 210, 212, and/or 214may be capable of performing a given measurement within the requiredaccuracy, while others may not. In addition, the respective systems 210,212, and/or 214 each have different throughput capabilities. Forinstance, the SEM 210 can measure about 30 wafers per hour (wph), thescatterometer 212 can measure up to 150 wph, and the spectroscopicellipsometer 214 may measure 75 to 80 wph. In accordance with an aspectof the invention, the robot 216 provides the wafers to the measurementinstrument which can provide the highest throughput, within the requiredmeasurement capabilities for a particular measurement task. In thisregard, the measurement capability requirements can be derived from theidentity of a particular wafer, which can be obtained, for example,using an OCR system (not shown) or other identification device ortechnique.

In this regard, the selection may also take into account theavailability or current utilization of the instruments 210, 212, and/or214 in scheduling the transfer of wafers via the robot 216. Thus, therobot 216 can provide a wafer to a selected measurement system 210, 212,or 214 having capabilities required for the wafer according to thecapabilities requirements information (e.g., obtained or derived fromthe wafer identification) and the measurement system capabilityinformation (e.g., whether a particular instrument 210, 212, and/or 214is capable of performing a particular measurement). Furthermore, theselection may reflect the measurement system 210, 212, and/or 214 havingthe highest throughput with the capabilities required for the waferaccording to measurement system availability information and throughputinformation. Thus, where the high throughput scatterometer 212 iscurrently being used to measure another wafer, the robot 216 mayadvantageously provide a wafer to the CD-SEM 210, even though this mayhave lower throughput capability. Alternative arrangements with moreload/unload stations afford additional flexibility in this regard forthroughput and performance optimization.

In addition, the measurement systems 210, 212, and/or 214 may becross-calibrated in order to facilitate alternating or switching betweenthe measurement systems. That is, calculated measurements generated bythe scatterometer 212 may be correlated to resemble the calculatedmeasurements provided by the CD-SEM 210. This cross-calibrationtechnique facilitates data interpretation to the extent that themeasurements generated by the scatterometer 212 for production samplescan be used interchangeably with those given by CD-SEM 210.

For example, a reference wafer (e.g., a focus-exposure matrix wafer ortest wafer) is measured with an integrated optical scatterometer 212 andscatterometry linewidth measurements are calculated in real time or byusing a database comparison approach or mathematical databasecomparison. For further description of the database approach, pendingU.S. application Ser. No. 09/927,177 (Publication No. 2002/0038196 A1)entitled “Database Interpolation Method For Optical Measurement ofDiffractive Microstructures” and filed on Mar. 28, 2002 is herebyincorporated by reference.

The wafer is also measured by the CD-SEM 210 to produce CD-SEM linewidthmeasurements. The relationship between the CD-SEM and the scatterometryline width measurements is mathematically analyzed and represented as apolynomial expression defining a continuous curve fit referred to as acorrelation function. The correlation functions may vary from processstep to process step (e.g., gate to contact) in the same fabricationprocess, so each process step may have its own correlation function. Thescatterometer may then be employed to measure linewidths on new andunknown wafers. The scatterometry linewidth is calculated as describedabove by comparing them to theoretical calculations. The calculatedlinewidth can then be adjusted with the correlation function in order tobecome a closer match with results expected if the CD-SEM 210 was used.

Referring now to FIGS. 6 and 7, the invention also provides forintegration of one or both of the APC system 206 and the process tool204 with the measurement system cluster. For example, in FIG. 6, anintegrated measurement system cluster 230 comprises the instruments 210,212, and 214, the robot 216, and the unloading and loading stations 220and 222. Another example is illustrated in FIG. 7, wherein an integratedsystem 240 comprises instruments 210, 212, and 214, the robot 216,unloading and loading stations 220 and 222, the APC system 206, and theprocess tool 204. In this example, it will be appreciated that thesystem 240 is not necessarily shown to scale, and that the process tool204 may be physically much larger than the other components in thesystem 240, in which case the integration may take the form of attachingthe clustered measurement components to the process tool 204. It will befurther appreciated that the integration of such components mayadvantageously reduce or eliminate the excessive physical transfer(e.g., sometimes manual) of wafers from one component to another, andthat the loading and unloading stations 222 and 220, respectively, maynot be needed in the system 240, as wafers from the process tool 204 canbe introduced directly to the robot 216.

The present invention thus provides for intelligent selection ofmeasurement instrumentation in order to provide timely measurementand/or inspection information and other feedback information notpreviously achievable. One example of such intelligent selection isillustrated in FIG. 8, wherein an exemplary measurement system selectionlogic component 250 is illustrated. The logic component 250 may operatein similar fashion to the measurement selection logic component 34 ofFIG. 1, as described hereinabove, whereby one or more selection criteriamay be used in making a selection from among two or more measurementinstruments or systems in a measurement system cluster (e.g., cluster 2of FIG. 1). For example, the selection logic component 250 may beimplemented in software, hardware, and/or combinations thereof, such asin a computer system (e.g., computer system 30 of FIG. 1).

The exemplary logic component 250 comprises various information used toprovide a measurement system selection 252 to a wafer transfer system254. For instance, capabilities requirements information 256 may bederived from a wafer identification 257, such as can be obtained from anoptical scan of one or more characters or codes stamped on a wafer, forexample, using an OCR system 258, as described above. The capabilitiesinformation 256 includes accuracies, and other parameters by which theselection logic component 250 may determine the suitability of one ormore measurement instruments for a particular measurement or inspectiontask. For example, the logic component 250 may compare the capabilityrequirements 256 for a particular task with measurement systemcapability information 261, 262, 263, and the like corresponding tomeasurement instruments (not shown) in a measurement system cluster(e.g., systems 10, 12, and 14 of FIG. 1), and determine which of themeasurement systems meets the capability requirements 256.

In addition, the measurement system selection 252 may also be based onmeasurement system availability or utilization information 271, 272,273, and the like corresponding with the measurement systems in thecluster. For example, the information 271, 272, and/or 273, and the likemay be consulted or queried in order to ascertain whether an instrumentis currently in use, about to be used, inoperable, scheduled formaintenance or the like. Thus, the wafer transfer system 254 may providewafers to another measurement system where a first such system iscurrently in use, whereby parallel or simultaneous measurement operationof two or more measurement systems in a cluster may further speed up themeasurement process from a cluster perspective. As a furtherconsideration, the selection logic component 250 may consult measurementsystem throughput information 281, 282, 283, and the like in order toadvantageously select an available measurement system having the highestthroughput capability. In a further addition, the measurement systemselection 252 may also be based on anticipated need based on fabricationschedule 260, e.g., for a fabrication process 80 as shown in FIG. 3.Fabrication schedule 260 may include information to allow intelligentsampling of the performance of particular process tools, e.g., 76 and79.

Another aspect of the invention provides methodologies for measuringprocess parameters in a semiconductor fabrication process. Referring nowto FIG. 9, and exemplary method 300 is illustrated in accordance withthe invention. Although the exemplary method 300 is illustrated anddescribed herein as a series of blocks representative of various eventsand/or acts, the present invention is not limited by the illustratedordering of such blocks. For instance, some acts or events can occur indifferent orders and/or concurrently with other acts or events, apartfrom the ordering illustrated herein, in accordance with the invention.Moreover, not all illustrated blocks, events, or acts, may be requiredto implement a methodology in accordance with the present invention. Inaddition, it will be appreciated that the exemplary method 300 and othermethods according to the invention can be implemented in associationwith the apparatus and systems illustrated and described herein, as wellas in association with other systems and apparatus not illustrated ordescribed.

Beginning at 302, a wafer is received at 304 from a fabrication process.For example, a wafer may be received in a measurement system cluster(e.g., system 2 of FIG. 1) from a process tool. At 306, the wafer isidentified (e.g., using an OCR system to read at least one characterthereon or by some other technique), and the measurement capabilitiesrequirements therefor are determined. Thereafter at 308, a determinationis made as to available measurement instruments (e.g., componentmeasurement devices in a measurement system cluster) having the requiredmeasurement capabilities. Such determination may take into considerationthe anticipated need based on the fabrication schedule. At 310, anavailable measurement instrument is selected having the requiredmeasurement capabilities and having the highest throughput capacity. Thewafer is then measured at 312 using the measurement system or instrumentselected at 312, whereafter the method 300 ends at 314.

Although the invention has been shown and described with respect tocertain illustrated implementations, it will be appreciated thatequivalent alterations and modifications will occur to others skilled inthe art upon the reading and understanding of this specification and theannexed drawings. In particular regard to the various functionsperformed by the above described components (assemblies, devices,circuits, systems, etc.), the terms (including a reference to a “means”)used to describe such components are intended to correspond, unlessotherwise indicated, to any component which performs the specifiedfunction of the described component (e.g., that is functionallyequivalent), even though not structurally equivalent to the disclosedstructure, which performs the function in the herein illustratedexemplary aspects of the invention. In this regard, it will also berecognized that the invention may include one or more computer systemsas well as computer-readable media having computer-executableinstructions for performing the acts and/or events of the variousmethods of the invention. Various modes of communication, e.g., betweencomponents of a computer system or between systems, are in some casesimplicit.

In addition, while a particular feature of the invention may have beendisclosed with respect to only one of several implementations, suchfeature may be combined with one or more other features of the otherimplementations as may be desired and advantageous for any given orparticular application. Furthermore, to the extent that the terms“includes”, “including”, with, “has”, “having”, and variants thereof areused in either the detailed description or the claims, these terms areintended to be inclusive in a manner similar to the term “comprising.”

1. A measurement system cluster for measuring process parametersassociated with wafers in a semiconductor fabrication process,comprising: first and second measurement systems having first and secondmeasurement instruments, respectively, wherein the first and secondmeasurement instruments are operative to measure at least one processparameter associated with a wafer; a wafer transfer system receiving awafer processed in the fabrication process; and a measurement systemselection logic component providing a measurement system selection tothe wafer transfer system according to a measurement system selectioncriteria and wherein the measurement system selection criteria comprisesat least one of capabilities requirements information associated withthe wafer, measurement system capability information associated with thefirst and second measurement systems, measurement system availabilityinformation associated with the first and second measurement systems,anticipated need for the first and second measurement systems, andthroughput information associated with the first and second measurementsystems and wherein the wafer transfer system selectively provides thewafer to at least one of the first and second measurement systemsaccording to the measurement system selection criteria for measurementtherein of a process parameter.
 2. The measurement system cluster ofclaim 1, comprising an optical character recognition system providing awafer identification to the measurement system selection logiccomponent, wherein the capabilities information is derived according tothe wafer identification.
 3. The measurement system cluster of claim 1,wherein the measurement system selection logic component provides themeasurement system selection indicating a selected measurement systemhaving capabilities required for the wafer according to the capabilitiesrequirements information and the measurement system capabilityinformation.
 4. The measurement system cluster of claim 1, wherein themeasurement system selection logic component provides the measurementsystem selection indicating a selected available measurement systemhaving the highest throughput with the capabilities required for thewafer according to the measurement system availability information andthe throughput information.
 5. The measurement system cluster of claim1, wherein the first and second measurement systems arecross-calibrated.
 6. The measurement system cluster of claim 1,comprising an APC system receiving a measured process parameter from theat least one of the first and second measurement systems and providingprocess feedback according to the measured process parameter.
 7. Themeasurement system cluster of claim 6, comprising a computer systemoperatively associated with the wafer transfer system and the first andsecond measurement systems, wherein the computer system comprises theAPC system.
 8. The measurement system cluster of claim 7, wherein thecomputer system comprises a measurement system selection logic componentproviding a measurement system selection to the wafer transfer systemaccording to the measurement system selection criteria, wherein thewafer transfer system provides the wafer to the at least one of thefirst and second measurement systems according to the measurement systemselection.
 9. The measurement system cluster of claim 8, wherein themeasurement system selection criteria comprises at least one ofcapabilities requirements information associated with the wafer,measurement system capability information associated with the first andsecond measurement systems, measurement system availability informationassociated with the first and second measurement systems, and throughputinformation associated with the first and second measurement systems.10. The measurement system cluster of claim 9, comprising an opticalcharacter recognition system providing a wafer identification to themeasurement system selection logic component, wherein the capabilitiesinformation is derived according to the wafer identification.
 11. Themeasurement system cluster of claim 9, wherein the measurement systemselection logic component provides the measurement system selectionindicating a selected measurement system having capabilities requiredfor the wafer according to the capabilities requirements information andthe measurement system capability information.
 12. The measurementsystem cluster of claim 11, wherein the measurement system selectionlogic component provides the measurement system selection indicating aselected available measurement system having the highest throughput withthe capabilities required for the wafer according to the measurementsystem availability information and the throughput information.
 13. Themeasurement system cluster of claim 12, wherein the computer systemcomprises calibration information associated with the first and secondmeasurement systems, and wherein the first and second measurementsystems are cross-calibrated.
 14. The measurement system cluster ofclaim 1, comprising an unloader station receiving the wafer from thefabrication process and operative to unload the wafer from a waferholding device and to provide the unloaded wafer to the wafer transfersystem.
 15. The measurement system cluster of claim 1, comprising aloader station receiving the wafer from the wafer transfer system andloading the wafer into a wafer holding device.
 16. The measurementsystem cluster of claim 1, wherein the wafer transfer system comprises arobot.
 17. The measurement system cluster of claim 1, comprising aprocess tool operative to perform at least one fabrication processingstep to the wafer and to provide the processed wafer to the wafertransfer system.
 18. The measurement system cluster of claim 17,comprising an APC system receiving a measured process parameter from theat least one of the first and second measurement systems and providingprocess feedback according to the measured process parameter.
 19. Themeasurement system cluster of claim 18, wherein the APC system providesthe process feedback to the process tool, and wherein the process toolperforms the at least one fabrication processing step according to theprocess feedback.
 20. A method of measuring a process parameterassociated with a wafer in a semiconductor fabrication process,comprising: receiving the wafer from the fabrication process;identifying the wafer; determining measurement capabilities required tomeasure the process parameter according to the identity of the wafer;selectively providing the wafer to at least one of a first and secondmeasurement systems according to the required measurement capabilitiesand measurement system capabilities information associated with thefirst and second measurement systems; and measuring the processparameter using the at least one of the first and second measurementsystems.
 21. The method of claim 20, wherein selecting the at least oneof first and second measurement systems comprises selecting an availablemeasurement system from the first and second measurement systems havingthe highest throughput with the required measurement capabilities forthe wafer according to measurement system availability information andthroughput information.